To ensure efficient flow of traffic it is important that the road network is in efficient condition and that the road users have up-to-date data about the current conditions and any exceptional arrangements. In prior art, data about traffic conditions has been acquired and distributed by means of a number of methods. The effect of weather on traffic conditions has been estimated on the basis weather forecasts as well as data from road weather cameras and weather sensors. Traditionally weather information has been transmitted to road users via radio and, recently, by means of various data terminal equipment. Additionally, along large roads information about slippery road conditions has been transmitted by means of large display billboards. A number of vehicles also include warning systems based on temperature sensors, vehicle stability control system or both, the systems providing the driver with warnings about possibly deteriorated driving conditions. There also are SMS-based services in which customers are provided with weather forecast or weather observation data at, e.g. certain intervals.
In addition to visibility the weather has an effect on driving condition as change of friction between the wheel of a vehicle or the like and road surface. The measurement of the said friction has been the subject of especial interest as it obviously has an immediate effect on the drivability of the vehicle. Defining the friction on the basis of weather observations has been challenging but the actual friction in existing conditions has been estimated in prior art technology by means of a number of acceleration sensor-based solutions. For example, EP 0461934 A2 discloses a slide observation apparatus of a four-wheel-drive car, the apparatus comprising e.g. sensors for longitudinal and transverse acceleration. EP 1452353 A2, on the other hand, discloses a slide observation arrangement for cars, the arrangement comprising three acceleration sensors so that the system includes a sensor for longitudinal, transverse and vertical directions.
The data produced by the acceleration sensors is in prior art processed by means of various arrangements. In the solution of EP 1475763 Al the data produced by the acceleration sensor is transmitted to the monitoring system of the vehicle analysing the data and transmitting video data in case of emergency to a monitoring company. There are also solutions in which the acceleration sensors are arranged to cooperate with other sensors. For example, U.S. Pat. No. 5,025,401 A discloses observation of sliding of the wheels of the vehicle based on differences between the measurement results of speed sensors and acceleration sensors. Further, US 2009/0210154 A1 is known, disclosing observation of sliding of a railroad vehicle, here based on simultaneous use of movement sensors, acceleration sensors and satellite positioning system.
Data has also been collected by state institutions, such as Finnish Road Administration about the effect of traffic congestion, accidents, road works and similar situations caused by road usage on the flow of traffic and the utilization rate of the roadways has been monitored, among others, by means of traffic cameras. Private parties have also acquired similar data. Data about exceptional conditions has also been transmitted via radio, but lately the data has also been transmitted to road users via navigation apparatuses and the Internet.
There are also projects in which data about the traffic rate is collected directly from the roads users. In a joint project by Berkeley University and Nokia the positioning data of the road users' mobile phones was used for determining the driving speed. On the project, the data obtained from the road users was transmitted to a central computer in which local travel times and congestion data were analysed for further distribution to various applications. In a practical deployment of the data acquisition and transmission was carried out by means of a program uploaded to the phone and anonymously sending GPS-based traffic data to the server.
Thus there are numerous ways of collecting and transmitting data essential to road users about driving conditions, especially the weather and congestion of the roads, both in a central as well as a distributed way.
Prior art has, however, some considerable drawbacks. Currently commonplace navigation systems that provide a real-time route guidance to a certain destination for the driver of a road traffic vehicle are usually based on GPS positioning and map data updated at intervals. The performance of the navigation systems in practical traffic situations, however, depends on local, sometimes quickly developing traffic limitations, such as especially the slipperyness caused by weather, but also traffic jams, accidents and similar unexpected changes in the transmission capacity of the road. If the database of the navigation systems can be quickly updated with data about the changed traffic limitations, the guidance can possibly be changed onto a new route almost immediately after the formation of the limitation. As has been stated above, the current systems receive periodically updated data about the traffic limitations. At best, the response time of the data is, however, of the order of 10 minutes or more. Especially the currently available slipperyness data are far too general to describe the drivability of a certain portion of road and usually they are based on a road weather forecast or deficient road weather measurements. Thus current systems can not quickly transmit reliable data about weather, more especially the real friction of the road surface.
Therefore, the aim of the present invention is to solve at least some of the problems of prior art and to produce a system capable of quickly and reliably transmitting extensive data about existing driving conditions to road users. An especial aim of the invention is achieve a minute level response time for communication.